Patent GB-665445-A (GB)
Title: Improvements in or relating to radio-beam navigation systems
IPC: G01S1/02
Filed: 1948-01-21
Abstract: 665,445. Radio navigation. SPERRY CORPORATION. Jan. 21, 1948 [Jan. 25, 1947], No. 1856/48. Class 40 (vii). A radio navigation system of the kind defining a path for a vehicle comprises a beacon consisting of a radio-frequency generator connected sequentially to two or more directive antennµ to radiate a number of overlapping beams and means for transmitting a reference signal synchronized with the sequential connection, and a receiver on the vehicle producing a first signal dependent on the position of the craft relative to the beams and the sequence of beam energization, and a second signal representative of the reference signal and combining these signals to produce an indication dependent on the comparative intensities of the overlapping beams as received and the position of the craft relative to the defined path. The beacon. In a system defining a path in a single plane two directive aerials are arranged to give overlapping patterns with equal intensity along the desired course and the output of a radio frequency generator applied to them in alternation. A reference signal synchronized with the aerial switching is also radiated as a modulation on a separate carrier, Fig. 1 (not shown). In a modification, the reference signal is applied by frequency modulation to the transmissions radiated by the directive aerials, Fig. 2 (not shown). The reference signal need not be used directly for this purpose but may be used to frequency-modulate a sub-carrier which itself modulates the directive beam transmissions, Fig. 4 (not shown). The receiver. A double receiver for azimuthal and vertical guidance which may operate with two beacons defining a guide line in these planes respectively, using different radio frequencies, comprises a local oscillator 20 and mixer 21 for obtaining I.F. signals from the received beacon signals. The azimuthal guidance I.F. signals are separated by amplifier 23 and correspond in amplitude with the signals received from the two transmitting antennµ modulated by a sub-carrier modulated by the reference signal. Amplitude detector 27 derives from these signals a waveform of the aerial switching frequency of zero amplitude on course and increasing in amplitude to either side thereof, the phase of which differs by 180 degrees on opposite sides of the course. Discriminator 25 in parallel with detector 27 produces a subcarrier frequency signal which is itself demodulated in discriminator 26 to give the reference signal which is of the same frequency as the output of detector 27. The outputs of units 27 and 26 are applied to phase-sensitive detector 28 which may be of double rectifier type and whose output is a D.C. voltage, the polarity of which depends on the sense of, and the magnitude of which is proportional to the magnitude of, the deviation of the craft from the path defined by the beams. The amplitude of the output is independent of the reference signal amplitude and is fed to one movement of cross-pointer meter 29. Signals from the other beacon are similarly treated and the output applied to the other pointer of the cross-pointer meter. In alternative indicating means replacing detector 28 and indicator 29, the reference signal is amplified, limited to constant amplitude, and applied to one winding of a centre zero wattmeter, the output of detector 27 being applied to the other winding, Fig. 9 (not shown). Specification 550,660 is referred to.